Why simple scrept takes time to run.....

Question

hello
i write simple block as
select consumer_number from receipts where consumer_number not in (select consumer_number from consumer_master);
in that receipts,consumer_master r table and both having consumer_number field
before some days i deleted same records from table receipts,consumer_master from that it takes time.
i checked index on both table but its ok.
plz help me.

Answer 1

790948 wrote:
RCI5142 @ msedcl> set autotrace TRACEONLY EXPLAIN
RCI5142 @ msedcl> select consumer_number from receipts where consumer_number not in (select consumer_number from consumer_master);
Execution Plan
0 SELECT STATEMENT Optimizer=ALL_ROWS (Cost=2903788 Card=18126
5 Bytes=2175180)
1 0 FILTER
2 1 TABLE ACCESS (FULL) OF 'RECEIPTS' (TABLE) (Cost=1153 Car
d=181272 Bytes=2175264)
3 1 INDEX (FAST FULL SCAN) OF 'PK_CON_NUMBER' (INDEX (UNIQUE
)) (Cost=20 Card=1 Bytes=12)
now what have to do this?You're doing a fast full scan on the index, which is probably better than a full table scan. CARD=1 means the subquery only expects to find one row - are your statistics current?
Try variations on the query - different ways of coding it to get the same result set. The first thing I think of is a correlated NOT EXISTS subquery (untested)
select consumer_number
  from receipts
where not exists (
             select 0
              from consumer_master cm
            where cm.consumter_number = r.consumer_number
);